Temperature compensated force and motion transmitting system



Feb. 16, 1954 MEICDUFF' 2,669,096

' TEMPERATURE COMPENSATED FORCE AND MOTION TRANSMITTING SYSTEM FiledMarch 1, 1950 MSG/M Patented Feb. 16, 1954 TEMPERATURE .COMPENSATEDYFORQE AND MOTION TRANSMITTING SYSTEM Stanley 1. MacDuiY, South Bend,Ind, assignor to Bendix Aviation Corporation, :South Bend, 11111., acorporation of Delaware Application March 1, 1950, Serial No. 147,025

.10 Claims. 1 This invention relates to a hydraulic mechanism and moreparticularly to a device which compensates for temperature variations ina force and motion transmitting system.

An important object of the invention resides in the provision of adevice capable of maintaining a predetermined pressure in a closedhydraulic system.

Another object of the invent-ion is to provide s. 'device "for use in ahydraulic system of the force and, motion type for maintaining the'pressure in said system at a fixed ratio with respect to the pressureof the source. 7 It is still further important object of the in ventionto provide a device to be interposed .between a fluid pressure sourceand a force and motion transmitting system for maintaining a fixedpressure ratio between the source and the system by connecting thesystem to the source at times when the pressure in the system dropsbelow a preselected value and exhausting fluid from said system when thepressure therein exceeds va preselected value.

The above and other objects and features of the invention will beapparent from the following description of the apparatus taken inconnection with the accompanying drawing which forms a part of thisspecification and in which the single figure represents diagrammaticallythe preferred form of invention.

"Referring now to the drawing I will first describe a fluid pressuresource which comprises a pump .ID having its inlet side connected to afluid reservoir I2 and its outlet side connected to an accumulator M viaa regulator or unloading valve it, the latter or which is capable ofbypassing fluid to the reservoir when the accumulator pressure reaches apredetermined value determined by the unloading valve setting. A reliefvalve I8 is interposed between the discharge side of the pump It and areturn line 20 to prevent excessive pressures from building up in line22 which connects the outlet of the pump to the unloading valve. Thereturn line 20 connects the unloading valve to the reservoir for return"line 2!).

ing device. Pistons 36 and 38, located in the transmitter and receiverunits respectively divide the cylinders of these units into opposedchame bers. A conduit 40, having a manually controlled valve .42therein, communicates the op posed chambers of the transmitter unit witheach other when the valve is open. A conduit 44, having a manuallycontrolled valve 45 therein, communicates the opposed chambers of thereceiver unit with each other when :the valve :46 is open.

It is a purpose of this invention to provide a valve device 58 whichwill maintain the fluid ressure in the closed system a fixed ratiowithrespect to the fluid pressure source. Variations of pressure in theclosed system might, for example, be caused by temperature variations.The valve device is connected to the source by a pi e line 52, and tothe pipe line 28, of the closed hydraulic system by a conduit 56. Afluid connection :55 extends from the valve device to the return line28. A pipe 58 having a :hand valve at therein communicates the pipe line28., of the force and transmitting system, to the A hand valve 62 islocated in the line .28 to be closed when the system is purged .a mannerto be hereinafter described. Under normal operating conditions the valve62 is open to permit communication between the transmitter and receiverunits.

The valve device 5t comprises a housing it provided with 'a stepped bore12, which a piston or plunger M is positioned for controlling thepressure in the force and motion trans mitting system. The plunger isformed so that the area of the large end 16 of the piston bears adefinite ratio to the area of the small end 18. This ratio is chosen tomeet the requirements of the system depending upon the maximum pressureavailable at the source and the pressure desired in the :closed system.A passage "'80, which communicates the intermediate section of the borewith one end of the large bore, is connected to the line :28 through thepipe 54. A passage 82, which has one end terminating in the intermediatesection of the bore and the other end of the passage connected to theopposite end of the bore, is adapted to communi-' small portion of theplunger is reduced at 86 so that when the valve device is in balance, asshown in the figure, the small piston covers one end of the passages 82and 84, thus cutting off communication between the fluid pressure sourceand the force and motion transmitting system.

Unwanted movement of the piston 38 of the receiver unit may causeserious damage, if the force and motion transmitting system is used inconnection with steering a vehicle, for example. Under certaincircumstances, such for example, if line 30 should be broken, thepistons 3-6 and 38 would be forced to the left and right ends of thecylinders 32 and 3A respectively thus moving the load to which thepiston 38 is connected. Since the load on the piston 35 will offer agreater resistance to its movement than will the unloaded piston 36, thelatter will be the first to move to the extreme position in theirrespective cylinders. To guard against this aforementioned danger novelmeans is installed for interrupting the supply of fluid to line 28. Thenovel means includes a normally open switch 96 secured to the left endof the cylinder 32. A stem 92, for actuating the switch, extends throughthe cylinder wall for engagement with the piston 36 when forced to theextreme left end of the transmitter unit to thereby close an electricalcircuit which energizes a normally open solenoid valve 94 located in theline 52, between the accumulator l4 and the reducing valve 50. Whenenergized the solenoid valve cuts oiT communication to line 28. Theelectrical circuit for energizing the solenoid is connected to anysuitable source of current, not shown.

Operation and function of the apparatus When replenishing or addingfluid to the force and motion transmitting system valve 62 is closed,and valves 42, 46, and Eli are opened. Under these conditions the piston14 is urged toward the top under the influence of the fluid pressuresource acting on the small end 18 of the piston, as viewed in thedrawing, thus communicating passage 82 with the pipe line 54. It canthus be seen that circulation through the entire closed hydraulic systemis accomplished, thereby purging the system of air, etc. Aftercompletion of the purging operation the valve 69 is closed firstfollowed by closing valves 42 and 46 after centering the pistons 36 and38, and finally opening the valve 62, thus preparing the system for use.

For the purpose of exempliflcation only, assume that the fluid pressuresource delivers fluid under 3,000# p. s. i. and the pressure in theforce and motion transmitting system is to be maintained at some p. s.i. With this requirement of the system in mind the piston is now formedso that the large end 16 is five times the area of the small end 18 or aratio of 5 to 1. Hence a pressure of 600# p. s. i. acting on the largeend of the piston will just balance 3,000# p. s. i. acting on the smallend of the piston. This condition of balance is illustrated in thefigure.

Assume an unbalance across the ends of the piston created by a reductionin pressure in line 28. The reduction in pressure might be caused by areduction in temperature or a leak in line 28 or 30. This will mean thatthe pressure of the fluid acting on the large end of the piston willhave been reduced, thus allowing the piston to move upwardly due to anunbalance, uncovering the passage 82, and communicating the passage 80,line 54, and line 28 with the 3,000# p. s. i. source via the reducedportion 86. Obviously this will move the piston downwardly so that thereduced portion 86 is now centered in the bore in a manner to cut offcommunication between the passages 82 and 80.

If the pressure in the line 28 due to a rise in temperature exceeds the600# p. s. i. the piston 14 will be forced downwardly from the neutralposition shown in the drawing, to thereby cause the reduced portion 86of the piston to communicate the line 28 with the return line 56 thusreleasing the excess pressure on the large end of the piston. The pistonnow moves upwardly under the influence of the 3,000# p. s. i. pressuresource until the total forces acting on the opposite ends of the pistonare balanced, at which time the piston will again assume the positionshown.

Although this invention has been described in connection with certainspecific embodiments, the principles are susceptible of numerous otherapplications that will readily occur to persons skilled in the art.

Having thus described the various features of the invention, what Iclaim as new and desire to secure by Letters Patent is:

1. In combination, a fluid pressure source, a double acting fluid forceand motion transmitting system including a pair of conduits connectingthe transmitter and receiver units, and means interposed between saidsource and one of said conduits for maintaining the fluid pressure insaid system at a fixed ratio with respect to the pressure source.

2. In combination, a fluid pressure source, a fluid force and motiontransmitting system including a pair of conduits connecting transmitterand receiver units, and a valve device capable of admitting fluid underpressure to one of said conduits from said source and also of releasingfluid from said one conduit to thereby maintain the pressure in thesystem at a predetermined value.

3. In combination, a fluid pressure source, a fluid force and motiontransmitting system including a pair of conduits connecting thetransmitter and receiver units, and a valve device conscious to thepressures of said source and in one of said conduits for automaticallymaintaining the pressure in the system at a preselected value.

4. In combination, a fluid pressure source, a fluid force and motiontransmitting system including transmitter and receiver units connectedtogether by a pair of pipe lines, and a valve device having connectionsto said source and to one of said pipe lines, said valve deviceincluding a moveable member for controlling flow between said sourceand. said system and responsive to a predetermined unbalance inpressures existing at said source and in said system for maintaining thepressure relationship therebetween at a prescribed ratio.

5. In combination, a fluid pressure source, a fluid force and motiontransmitting system including transmitter and receiver units connectedtogether by a pair of pipe lines, and a valve device for keeping thefluid in one of said pipe lines at a predetermined pressure with respectto said pressure source and having connections to said source, to areturn, and to said one pipe line, said valve device comprising valvemeans conscious to the pressures of the source and in said one pipe linefor communicating said one pipe line with either said source or saidreturn.

6. In combination, a fluid pressure source, a fluid force and motiontransmitting system including transmitter and receiver units connectedtogether by a pair of pipe lines, and a valve device for keeping thefluid in one of said pipe lines at a predetermined pressure with respectto said pressure source and having connections to said source, to areturn, and to said one pipe line, said valve device including a memberconstructed and arranged to control the fluid in said connections andresponsive to the diflerence in pressure of the source and in said onepipe line.

7. In combination, a fluid pressure source, a fluid force and motiontransmitting system including transmitter and receiver units eachprovided with a piston, a connection between said source and system, andmeans in said connection for controlling fluid under pressure to saidsystem, said means being responsive to movement of the transmitter unitpiston to an extreme position for cutting off the system from saidsource.

8. In combination, a fluid pressure source, a fluid force and motiontransmitting system ineluding transmitter and receiver units eachprovided with a piston, means for controlling communication between thesystem and the pressure source comprising means carried by saidtransmitter unit and connected to said first named means for causingactuation thereof upon movement of said transmitter piston to an extremeposition, to thereby cut off the pressure source.

9. In combination, a fluid pressure source, a fluid force and motiontransmitting system including transmitter and receiver units, a fluidcontrol device interposed between the source and system, and meanscarried by said transmitter unit and connected to said control unit foractuating the same upon predetermined movement of said transmitter,whereby the system is cut off from the source.

10. The combination with a fluid force and motion transmitting systemincluding transmitter and receiver units interconnected by two fluidpassages, of means connectable to a fluid pressure source, to a return,and to one of said fluid passages for maintaining the fluid pressure insaid system at a fixed ratio with respect to said source, said meansincluding a valve device provided with a moveable member on which thepressure from the source acts in one direction and on which the pressureexisting in said one fluid passage acts in the opposite direction, saidmember being responsive to a predetermined unbalance in pressurethereacross for controlling flow between said one of the fluid passagesand the source on the one hand and between the said one fluid passageand the return on the other hand.

STANLEY I. MACDUFF.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,207,944 Richardson July 16, 1940 2,229,109 Martin Jan. 21,1941 2,431,032 Ernst Nov. 18, 1947 2,432,305 Geiger Dec. 9, 19472,487,716 Majneri Nov. 8, 1949 2,506,093 MacDufi May 2, 1950 2,551,274MacDuff May 1, 1951

